For a speech with such profound consequences for domestic British politics,
David Cameron’s European address arguably found its most important audience
abroad.

The calculus that underpins Prime Minister’s strategy is this: the more concessions he wins from the rest of the European Union when renegotiating Britain’s membership, the more British voters – and, critically, the more Conservatives – will join him in 2017 in voting for that membership to continue.

That was why the speech was always intended to be made outside Britain, as geographic proof that Mr Cameron is serious when he says that his true intent is not to leave Europe but to reform it. Events conspired against that plan, but the point stands: to get the deal that he has promised to promote “with heart and soul”, Mr Cameron needs other EU leaders’ help.

So the speed and stridency of the French response to Mr Cameron’s speech was striking: minutes after he spoke, Laurent Fabius, the French foreign minister, was criticising a “dangerous” policy and insisting that Mr Cameron’s existential challenge to “ever closer union” must fail. For the French, you don’t join a football club then try to play rugby.

Mr Cameron can expect more of the same, in spades, in Brussels next month when painful talks about the EU’s budget for 2014-20 resume. Mr Cameron wants to cut European spending, but why, his opponents will ask, should anyone listen to a man whose country may not even be at the table when that budget round is over?

Yet the French response was anticipated in London, and largely discounted as a result. For those who helped craft the speech, one European response mattered more than any other: Angela Merkel’s. Germany is Europe’s dominant power and its chancellor is Europe’s dominant leader. Her willingness and ability to accommodate Britain’s desire for a rebalanced relationship is critical. Mr Cameron has staked a lot on his belief that ultimately, she will back him to keep Britain in the EU.

Her reaction has raised cautious Conservative hopes that his gamble will pay off. While her Liberal foreign minister accused Mr Cameron of trying to “cherry-pick” the EU deal, the Christian Democrat chancellor was more emollient. Yes, she cautiously noted that the EU only ever proceeds by compromise, and warned Mr Cameron that he is not the only leader with “wishes”. But she did not dismiss him. She promised to talk.

Mr Cameron would prefer that discussion to produce a whole new EU treaty – why not the London Treaty? -- a document codifying his pro-market reforms. But many other leaders are wary of yet another new treaty, and Mrs Merkel has cooled on the idea. Hence Mr Cameron says Britain is ready to proceed without a new treaty: anything to keep Mrs Merkel talking. Only by talking can Mr Cameron hope to win back British control on employment rules, market regulation, farming, and maybe even a few aspects of immigration policy: enough to present in 2017 as a “new settlement” for Britain. In exchange, Mrs Merkel will expect British backing for German ideas on financial regulation and economic coordination within the eurozone, and support for the sort of trade liberalisation and labour market reforms that France’s Socialist government will resist.

Mr Cameron’s big speech has started a big conversation with Mrs Merkel. It will last for many years and it will not always be easy. And it will likely decide both his political fate and Britain’s place in Europe.